Bartonella henselae is an important cause of illness in both immunocompromised and non-immunocompromised humans; infection with this organism can lead to bacillary angiomatosis, peliosis hepatis, bacterimia, endocarditis and fever. In immuno- competent people , B. henselae has been demonstrated to cause cat scratch disease (CSD), a persistent, necrotizing inflammation of the lymph nodes. CSD is probably the most common Bartonella infection in the United States, estimated to occur in 22,000 people and to result in health care expenditures of at least 12 million annually (8). Bartonella henselae appears to be transmitted from infected cats to humans largely by the cat flea (1,7). The cat serves as a reservoir host for B. henselae, and the organism has been found within feline erythrocytes (9). Cats appear to be very efficient reservoir hosts for infection with B. henselae and this conclusion is based upon screening naturally infected populations and determining that a high percentage of cats are seropositive and asymptomatically infected. Experimentally infected, untreated cats remain asymptomatic and bacteremic for 1 year or longer. Valuable information has been obtained from the cat model unfortunately, no bacillary angiomatosis has ever been identified in the cat model of disease. We believe that the absence of this disease manifestation in the cat may be due to the fact that all previous studies have not properly taken into account a potential environmental temperature requirement of the bacteria. Temperature requirement for primary and/or secondary lesion formation, has been well documented and demonstrated with Treponema pallidum and more recently, with Haemophilus ducreyi. Given the temperature dependant nature for optimal in vitro growth conditions of B. henselae (35 ?C)(5) we believe that initial papule formation and later, bacillary angiomatosis formation may be dependant upon external temperature of the skin. We are currently testing if a rabbit model of disease for Bartonella henselae can be constructed. This study is important because at this time the cat model does not adequately represent all of the clinical manifestations that are present in the human infection. In addition, cats are more expensive and labor intensive to work with than rabbits.